Medical devices such as capsule medical devices are swallowable medical devices that are swallowed by a subject to enter the subject's body, where they traverse a passage in the body cavity to capture images of a target site inside the passage in the body cavity. The capsule medical devices described above have a configuration in which an image-acquisition device that can perform the above-described medical procedure, for example, a CCD (Charge Coupled Device) that can acquire images or the like, is provided for performing image acquisition at the target site inside the passage in the body cavity.
However, the above-described capsule medical device has to be guided through the body cavity in order to reach a target site. To guide the capsule medical device, it is necessary to detect its position in the body cavity.
Therefore, techniques for detecting the position of capsule medical devices guided to sites whose positions cannot be visibly confirmed (body cavities or the like) (for example, refer to Patent Document 1) are proposed.
Patent Document 1:    PCT International Publication No. WO 2004/014225 Pamphlet
Patent Document 2:    U.S. Pat. No. 7,026,927